Pump for Liquids Under Positive Pressure

Abstract

A pump for liquids at positive pressure, includes a pump chamber (18) accommodating an impeller (24), wherein the impeller (24) is axially biased against a non-rotating support element (48) which determines the axial position of the impeller (24). The shaft (42) may be coupled to a drive shaft (64) through a magnet coupling (56, 62).

Description

The invention relates to a pump for liquids under positive pressure, comprising a pump chamber which accommodates an impeller.

When pumping a liquid at a temperature above its boiling point, a high pressure must be maintained in order to prevent the liquid from evaporating. Thus, for example, for hot water having a temperature of 120° C., a pump must operate at a pressure of, for example, 0.25 MPa (2.5 bar), without any pressure losses. It can be assumed that, for an increase in temperature of 10° C., the pressure must be increased by approximately 0.1 MPa.

In order to maintain such a high pressure during operation of the pump, in case of an impeller-type pump, small tolerances must be provided for the spacing between the impeller and the adjoining walls of the pump chamber. If the play is increased by 1/10 mm, for example, the pressure may be reduced by 0.1 MPa. On the other hand, a certain minimum spacing is necessary in order to limit the wear of the impelled which is mounted on a floatingly supported shaft. As a result, the allowable hot water temperatures are limited by the increase of wear of the impeller.

It is an object of the invention to provide a pump of the type indicated above, which operates with as little wear as possible when pumping liquids, and which at the same time permits to maintain a high pressure.

According to the invention, this object is achieved by the feature that the impeller is axially biased against a non-rotating support element which determines the axial position of the impeller. Since the axial position of the impeller is determined by the support element, the dimensions of the pump chamber and the impeller can be adapted one another with very high precision, so that a very small gap between the impeller and the walls of the pump chamber can be maintained. Thus, for example, the pump is suitable for pumping hot water at high temperatures and at correspondingly high pressures.

Further developments and useful details of the invention are indicated in the dependent claims.

Preferably, the impeller is fixed on a shaft which is axially biased against the support element. Thus, a sliding rotary motion between the shaft and the support element occurs on a small radius, so that the frictional resistance is reduced. For further reducing the friction, the shaft and the support element are preferably made of a ceramic material.

Preferably, the shaft is supported in at least one radial slide bearing. Accordingly, the radial position of the impeller can also be defined with high precision. In order to reduce dynamic friction, the shaft and the slide bearing are preferably made of a ceramic material. The shaft is displaceably supported in the bearing, so that it is possible to axially bias the shaft and the impeller, respectively, against the support element.

Preferably, the support element and the at least one slide bearing are flushed with the liquid to be pumped, when the pump is operating.

Preferably, a flush passage passing through a wall of the pump chamber for flushing the at least one slide bearing connects a pressure-side region of the pump chamber with a region situated beyond the slide bearing. In this way, the slide bearing can reliably be flushed with the liquid being pumped.

In a preferred embodiment, a flush passage for flushing the at least one slide bearing is formed by a passage passing axially in the shaft. This passage may be provided in addition to the flush passage formed in the wall of the pump chamber.

Thanks to the flush passages according to the invention, the pump may be operated not only with a horizontal axis of rotation of the impeller but also in a suspended position, i.e. with a vertical axis of rotation of the impeller.

Preferably, a radial play between the impeller and the pump chamber is not larger than 1/10 mm. This corresponds to an average distance between the impeller and a wall of the pump chamber of 5/100 mm. It is particularly preferred that the play amounts to not more than 5/100 mm, corresponding to an average spacing of 0.025 mm.

Preferably, an axial spacing between the impeller and the pump chamber on both sides of the impeller is not larger than 1/10 mm. More preferably, this spacing amounts to not more than 5/100 mm, particularly preferred is a spacing of 3/100 mm or less.

The temperatures and pressures that are allowed for the pump according to the invention can be increased further, by dispensing with seals at the rotating parts. According to a further development of the invention, the shaft is coupled to a drive shaft by a magnet coupling, wherein a first coupling member of the magnet coupling is connected to the shaft, a second coupling member of the magnet coupling is connected to the drive shaft, and a wall, which seals the drive portion of the pump against a portion accommodating the shaft and the pump chamber of the pump, passes through a gap between the first and second coupling members.

By utilising the magnet coupling, seals at the rotating parts can be dispensed with, because no contact between the first and second coupling members occurs in the gap of the magnet coupling. Thanks to this, the pump may operate for example in a pressure range from 0.6 to 0.65 MPa, so that hot water at a temperature of 160° C., for example, may be pumped. Such temperatures are not allowable in conjunction with conventional rubber seals, for example.

It is particularly preferred that the first and second coupling members are so arranged relative to one another that the magnet coupling urges the shaft axially against the support element. Thus, the magnet coupling fulfills two functions. On the one hand, it permits to seal the portion of the pump, which contains the liquid to be pumped, by a closed wall, so that no seals need to be employed at the rotating parts. On the other hand, it assures that the impeller and the shaft, respectively, are axially biased against the support element.

In another embodiment of the invention, the shaft is axially biased against the support element by a compression spring. The compression spring may also be used when a magnet coupling is provided.

Preferred embodiments of the invention will now be explained in conjunction with the drawings, wherein:

FIG. 1 is a partial section of a first embodiment of a pump having a magnet coupling; and

FIG. 2 is a partial section of a second embodiment of a pump having a slip-ring seal and a compression spring.

The pump shown in FIG. 1 has an essentially cylindrical casing 10 to which an intermediate member 12 is flanged at the lower end thereof, and a head member 14 is flanged to the intermediate member. These members are screw-tightened to the casing 10 by means of bolts 16 which pass through the head member 14. In the intermediate member 12 and the head member 14, a pump chamber 18 is formed, which extends between the intermediate member 12 and the head member 14 in the shape of an interrupted ring and connects an intake passage of an intake pipe, which has not been shown, to an outlet passage 20 of an outlet pipe 22. In the sectional view shown in FIG. 1, the outlet passage 22 formed in the intermediate member 12 is positioned behind the plane of the drawing, whereas the intake passage, which has not been shown, is formed in the head member 14 and is situated in front of the plane of the drawing.

The pump chamber 18 accommodates an impeller 24 having a disk-shaped central portion 26 and impeller blades 28, 30 which are arranged above and below the central portion 26 and each extend radially into an outer region of the impeller 24. The blades 28 arranged above the central portion 26, i.e. on the side of the outlet passage 20, are slightly displaced rearwardly in the direction of rotation of the impeller 24 relative to the blades 30 provided below the central portion 26. The blades 28 extend axially upwardly up to an upper face 32 of the impeller 24. The blades 30 extend axially downwardly up to a lower face 34 of the impeller. On the radially inner side of the pump chamber 18, the upper face 32 approaches a wall formed by the intermediate member 12 and forms therewith a gap of, for example, 2/100 mm, whereas the lower face 34 approaches a wall formed by the head member 14 and forms therewith a gap of, for example, 3/100 mm.

The blades 28, 30 and the central portion 26 of the impeller 24 extend radially outwardly up to a straight outer periphery 36 of the impeller 34. The outer periphery 36, in the range between the end of the pump chamber 18 at the outlet passage 20 and the start of the pump chamber 18 at the intake passage, has a lateral spacing of only 0.025 mm from a wall that is formed for example by the head member 14. Thanks to the small lateral and axial spacings between the impeller 24 and the surrounding walls, the pump is capable of maintaining a very high pressure.

The impeller 24 is fixedly mounted by means of a sleeve-type projection 38 and by means of tolerance rings or corrugated rings 40 on a shaft 42 that is made of ceramic material. Below the impeller 24, the shaft 42 is supported in a slide bearing 44 that is fixed in the head member 14 with a corrugated ring 46. The slide bearing 44 is made of a ceramic material, e.g. silicon carbide.

At its lower end, the shaft 42 is slidingly supported on a ceramic support element 48 that is formed for example by a perforated disk of tungsten carbide and is fixed to the head member 14 with a bolt 50.

Above the impeller 24, the shaft 42 is guided in another slide bearing 52 which is fixed at the intermediate member 12 with a corrugated ring 54. The shaft 42 is slidingly guided in the slide bearings 44, 52.

A first coupling member 56 of a magnet coupling is fixed to the top end of the shaft 42 with a corrugated ring 58. The first coupling member 56 extends in an annular shape around the end of the shaft 42 and is surrounded with a spacing by an annular flange 60 of a second coupling member 62 of the magnet coupling. The second coupling member 62 is fixed at the lower end of a drive shaft 64 that is supported at the casing 10 with a fixed bearing 66. The drive shaft 64 is driven by a motor of the pump.

A separating can 68 is arranged in a pot-shaped hollow space formed between the coupling members 56 and 62, the separating can having a very small wall thickness in the region of an annular gap 70 formed between the first coupling member 56 and the flange 60.

The separating can 68 forms a wall made of a non-magnetic material, e.g. of VA steel. It is sealed against the intermediate member 12 with a sealing ring 72, and the intermediate member 12 is again sealed against the head member 14 with a sealing ring 74. In this way, a closed hollow space is formed, which encompasses the pump chamber 18 and is open only at the intake passage and the outlet passage 20.

At the annular gap 70, magnet elements 76 arranged in the first coupling member 56 are opposed to magnet elements 78 that are arranged in the flange 60. They magnetically transmit a drive torque from the drive shaft 64 onto the shaft 42 and hence onto the impeller 24. The magnet elements 76 and 78 are axially offset relative to one another in such a way that they exert an axial force onto the shaft 42, which urges and biases the shaft 42 against the support element 48. In this way, the axial position of the impeller 24 relative to the head member 14 and thus also relative to the intermediate member 12 is defined exactly, so that, in spite of the very small axial spacings, no contact will occur between the impeller 24 and these members. For this reason, the pump operates with very little wear.

A flush passage 80 starts in the vicinity of the outlet-side end of the pump chamber 18, passes upwardly through the intermediate member 12 and opens in the region of the coupling member 56. The flush passage 80 is formed by a straight bore which is tapered at the lower end, so as to limit the flow into the flush passage.

One purpose of the liquid that is driven upwardly through the flush passage 80 is to flush the slide bearing 52. Moreover, this liquid is forwarded through a passage 82 in the form of an axial through-bore of the shaft 42 to the lower end of the shaft, where the liquid exits laterally through grooves 84, that have been indicated in chain lines, and serves to flush the slide bearing 44.

The embodiment of the pump shown in FIG. 2 differs from the one shown in FIG. 1 especially by that it has no magnet coupling. Like or similar parts are designated by like reference numerals.

The impeller 24 is fixed on a shaft 86 with corrugated rings 40, the shaft 86 being supported at its lower end in the slide bearing 44 and being supported on the support element 48 like the shaft 42 in FIG. 1. At the upper end, however, the shaft 86 is reduced in diameter, passes through a bore 88 of the intermediate member 12 and is coupled to the drive shaft 64 by a tappet sleeve 90. A gap between the shaft 86 and the bore 88 is sealed by a slip-ring seal 92 at a seal face 94. Via a sleeve member 96, the slip-ring seal 92 is pressed upwardly against the seal face 94 by a compression spring 98 the lower end of which is supported on a shoulder of the shaft 86.

Since the shaft 86 is slidingly guided in the tappet sleeve 90, the slip-ring seal 92, the sleeve member 96 and the slide bearing 44, the compression spring 98 will at the same time urge the shaft 86 downwardly against the support element 48. In this way, the exact axial position of the impeller 24 relative to the head member 14 and the intermediate member 12 is defined, similarly as in the first embodiment.

Again, the small spacings between the impeller 24 and the adjoining walls of the pump chamber 18, as mentioned above, are made possible by the exact axial and radial positioning of the impeller 24. Thanks to this, the pump operates with very little wear, and very high temperatures and pressures of the liquid to be pumped are possible, in spite of the use of a slip-ring seal at the rotating shaft 86. Thus, for example, it is possible to pump hot water at a temperature in the range of 120 to 130° C.

For flushing the slide bearing 44, a cross bore 100 is provided in the sleeve-type projection 38 and in the shaft 86 above the impeller 24, and the cross-bore opens into a passage 102 formed by an axial bore of the shaft 86, through which liquid for flushing the slide bearing 44 is again supplied from the upper portion of the intermediate member 12 towards the lower end of the shaft 86, where it exits through the grooves 84.

A vent and flush passage 104 extends in a height approximately below the slip-ring seal 92 from the upper portion of the head member 12 to the outlet passage 20 and passes through a web 106 formed at the outlet pipe 22.

The described embodiments of the pump have the outstanding feature that the constructions of the head member 14 and of the casing 10 and the drive shaft 64 are identical, and that, in each case, the lower part of the pump comprising the intermediate member 12, the head member 14, the impeller 24 and the shaft 42 and 86, respectively, can be removed for maintenance purposes. Further, this makes it possible to convert the one embodiment of the pump into the other one by exchanging the lower part of the pump. The dividing line, where the exchangeable part is fitted to the upper part of the pump, is always located outside of the range of the liquid to be pumped.

Claims

1. Pump for liquids at positive pressure, comprising: an impeller,at least one pump chamber accommodating the impeller,a non-rotating support element, andthe impeller is axially biased against the non-rotating support element which defines an axial position of the impeller.

2. Pump according to claim 1, further comprising a shaft which is axially biased against the support element, andwherein the impeller is fixedly mounted on the shaft.

3. Pump according to claim 1, further comprising at least one radial slide bearing which supports the shaft.

4. Pump according to claim 3, further comprising a flush passage passing through a wall of the pump chamber for flushing said at least one radial slide bearing and which connects a pressure-side portion of the pump chamber to a portion situated beyond the slide bearing.

5. Pump according to claim 3, further comprising a flush passage for flushing said at least one slide bearing and which is formed by a passage which passes axially through the shaft.

6. Pump according to claim 1, wherein a radial play between the impeller and a wall of the pump chamber amounts to not more than 1/10 mm.

7. Pump according to claim 1, wherein, on both sides of the impeller, an axial play between the impeller and a respective wall of the pump chamber amounts to not more than 1/10 mm.

8. Pump according to claim 1, further comprising: a magnet coupling for coupling the shaft to a drive shaft, the magnet coupling including a first coupling member connected to the shaft, and a second coupling member connected to the drive shaft, anda wall, which seals a drive-side portion of the pump against a portion accommodating the shaft and the pump chamber, passes through a gap between the first and second coupling members.

9. Pump according to claim 8, wherein the first coupling member and the second coupling member are arranged in such relative positions that the magnet coupling biases the shaft axially against the support element.

10. Pump according to claim 1, further comprising a compression spring which axially biases the shaft against the support element.